Gull

I

Introduction

Gull, common name for approximately 47 species of long-winged, web-footed seabirds, the most familiar birds of the seashore. The commonly used name seagull is a misnomer. Many species nest or feed inland, and most of the rest are strictly coastal; only the kittiwakes are truly oceanic during the non-breeding season. Gulls are distributed throughout the world, excluding only tropical deserts and jungles, the central Pacific islands, and most of Antarctica. Some gulls are migratory.

II

Characteristics

The sizes of gulls, from bill to tail, range from 27 to 80 cm (11 to 31 in). The bill is hooked. Except for the totally white ivory gull, the birds vary from pale grey to black above, and from white to grey below. The heads of many have black, grey, or dark brown hoods during the breeding season. Many of the grey-winged species have black or darker grey wing-tips, often with white spots. The sexes are alike in colour. The young have mottled brown or grey plumage, taking as long as four years (in the larger species) to attain the definitive adult coloration through a progressive series of annual moults.

Gulls are equipped for versatility rather than specialization. For example, their wings are good for soaring as well as for strong and agile powered flight, but they cannot use air currents as efficiently as albatrosses or fly as fast as falcons. The foraging of gulls includes fishing, scavenging, egg predation, insect catching, following ploughs for earthworms and ships for rubbish, dropping shellfish from a height to break them open, and foot paddling to stir up organisms in shallow water.

The common gull, found throughout Eurasia, North Africa, and western North America, is regularly seen feeding inland. The 40-cm (16-in) long bird has a plain white head and light grey back. The herring gull is larger, 60 cm (24 in) long, and is distributed throughout the northern hemisphere where it is noted for its scavenging. Restricted to the coastal areas of southern and western Australia is the Pacific gull, which has a large head and bill. Its head and bib are white and its back is black.

III

Life Cycle

Gulls breed in colonies, mostly on the flat ground of beaches, marshes, or riverbeds, where they build simple, shallow, grass-lined nests. Several species nest on ledges of cliffs, notably the kittiwakes. The clutch consists of two or three greenish-brown, speckled eggs, which take 20 to 30 days to incubate. At hatching the chicks have down feathers, and the eyes are open. Chicks can stand, but are dependent on their parents for food and warmth. The parents share in incubation of the eggs and in the brooding and feeding (by regurgitation) of the chicks, which fledge between four and six weeks after hatching. Gulls have been known to live as long as 40 years in captivity and as long as 36 years in the wild.

IV

Behaviour

Territory defence, pair formation, parent-chick interactions, and other gull activities involve communication behaviour consisting of postures, movements, and calls, some of which are quite complex both in form and in function. For example, courting gulls perform threat displays, but they do so in sequences that apparently modify the meaning of the display. Recognition of one individual by another by such means has been demonstrated experimentally. Pair bonds may be long-lasting.

Gulls may thrive at the expense of other species. For example, larger gulls are known to drive out smaller gulls and terns from nesting territories, partly through egg and chick predation. The scavenging of gulls, including herring gulls, can also affect the ecology of urban environments. Airfields (and the rubbish dumps that are commonly located near them) attract large numbers of gulls, which present a collision hazard to aircraft; this problem has yet to be solved. In some places, gulls’ eggs are collected for food.

Scientific classification: Gulls belong to the family Laridae in the order Charadriiformes. The common gull is classified as Larus canus, the herring gull as Larus argentatus, and the Pacific gull as Larus pacificus.